Head and neck cancer (HNC) survivors experience a significant financial burden (FB) after treatment, even in Germany with a statutory health insurance. The financial toxicity of cancer can cause higher morbidity and mortality rates but may also impair quality of life (QoL). Our investigation aims to elucidate the impact of HNC-related FB on QoL potentially facilitating better understanding of their interplay. Of n = 209 consecutive HNC patients attending our university hospital’s cancer aftercare program between August 2022 and March 2023, n = 200 patients completed the EORTC QLQ-Q30 questionnaire, and we analyzed the QoL scale data based on their self-reported FB. Parametric and non-parametric analyses were used to assess the impact of FB and independent predictors on QoL and QoL scales, and causal diagrams were used to visualize their causal relationship. HNC patients reported significant impaired QoL in consequence of FB. Significant detrimental effects of FB were observed on role functioning (RF; p = 0.0011), emotional functioning (EF; p = 0.0039), cognitive functioning (CF; p = 0.0149), and social functioning (SF; p = 0.0011). Advanced stage, advanced T category, and suffering from larynx/hypopharynx cancer demonstrated a significant quantitative interaction with FB increasing the risk for impaired QoL with respect to RF, EF, CF, and SF. HNC survivors suffer from significant impaired QoL and FB after treatment. In general, FB impairs particular QoL scales, and these QoL scales are differentially affected by particular tumor characteristics together with FB jointly impairing QoL of HNC survivors.